1. Field of the Invention
The present invention relates to an output circuit, and more particularly, to an output circuit with external transistors.
2. Description of the Related Art
A subscriber line interface circuit (SLIC) of an exchange employs a power supply circuit. The power supply circuit has an output circuit for handling a large amount of power. When integrating the output circuit, power consumed by the output circuit, i.e., an output drive circuit or output transistors, cannot be ignored. The integrated output circuit needs a package of low heat resistance that may increase cost and size. In particular, a high-function LSI with many pins will be very expensive if it must employ such a special package because of the output circuit thereof.
Integrating an output circuit into an LSI or IC may be advantageous to reduce the number of parts. Employing a small number of external parts, however, does not hinder the compactness of a semiconductor product owing to an improvement in an SMD technique. Accordingly, it is sometimes advantageous to employ an output circuit with external transistors if requirements on power, voltage, and current allow. In this case, the important thing is to secure the performance of the output circuit with external transistors. The problems of the prior art will be explained in detail with reference to accompanying drawings.